Microstructure and phase transformations of silica glass and vanadium oxide by severe plastic deformation via high-pressure torsion straining

Plastic deformation of oxides is generally difficult due to their hard and brittle nature resulting from their covalent or ionic bondings. In this study, severe plastic deformation was successfully introduced in SiO₂ glass and crystalline VO₂ by high-pressure torsion (HPT). SiO₂ glass transformed to a denser amorphous phase without showing any crystallization after processing in the temperature range of 300–723 K. Crystalline VO₂ transformed from the coarse-grained monoclinic phase to a nanograined triclinic phase with insulating electrical properties by plastic strain effect. These findings indicate the potential of HPT process in tuning the crystal structure of optical and electrical oxides.